First, welcome to the board, even though it is for a disconcerting reason. The women here are wonderful and will help.
Second, call the doctor and if for no other reason ask for a referral to a surgeon. Sometimes when a cyst or lymph node is very large they should be removed. I am not sure about the lymph node, but someone here will be able to tell you. Your history of fibrocystic breast condition is usual as you know. Don't be afraid and not call anyone to get more medical care. That is the worst thing you can do. My DS and DM have fibrocystic breast and have had to have some benign cysts removed and they are fine. You know it is benign and that is a good thing. But, please let a surgeon look at your tests and talk with you.
Do some research on lymph nodes and be prepared to ask questions. The more you know the better you will feel.
Let us know what happens and get on the phone.